This invention relates to a process for purifying a low polluted water, in which heavy metals, such as iron contents and manganese, and very fine suspended matters (these are all hereinafter referred generally to as "inadequate matters") concurrently or selectively contained in the low polluted water are continuously removed to provide a highly purified water, as well as, to an apparatus for practicing the process.
In those areas poorly equipped with water service, well water is used singly or in combination with service water so as to cope with lack of water during summer or with the raise in the water charge. In the case of well water, those which were proved to conform with the standard quality of drinking water analysis carried out by an organization such as public health center are used as drinking waters for human. However, depending on the configuration of the ground in which wells are bored, the well waters sometimes contain heavy metals such as iron contents and manganese in an amount beyond the allowable level. While the iron contents do not undergo oxidation in the underground water containing a low level of oxygen, they are oxidized upon contact with oxygen when pumped up to the ground surface, causing so-called a state of red water. Such well water containing a high level of iron contents is not generally suitable as the drinking water for human.
Meanwhile, in the case of service water, a water is subjected to sedimentation and filtration treatments in a large scale purifying facility, as well as, to sterilization treatment using chlorine and the like before distributed throughout a city. However, if a large amount of heavy metals such as iron contents and manganese are contained in the raw water for water service and water consumption sometimes jumps up like during summer, the dwell time of the raw water in the purifying facility where it is subjected to sedimentation and filtration becomes short. Accordingly, an insufficiently treated water still containing some amount of heavy metals such as iron contents and manganese is supplied generally to every household etc. Thus, the service water during summer comes to contain a particularly large amount of iron content and tastes bad.
For example, if such well water containing a large amount of iron content is used as an industrial water, rusting occurs in the piping system of machinery and the like to cause corrosion or clogging in the pipes, giving serious damage in the maintenance of the equipments. Meanwhile, it is known in the field of stockbreeding, if such well water containing a large amount of iron contents is used as such as a drinking water for cows and pigs, the iron contents react with phosphoric acid etc. in their bodies to make the animals to have acidic constitution, inhibiting absorption of nutrients and affecting normal growth of the animals. Further, if such water containing a large amount of iron contents, manganese, etc. is used for irrigation in the field of agriculture, horticulture, etc., the mineral composition in the soil is ill-balanced to inhibit absorption of nutrients by fruits, vegetables and garden plants, causing troubles such as depauperation or suffering from various diseases due to reduction in the resistance to the pathogenic bacteria. Therefore, it is desirable to remove the inadequate matters including iron contents and manganeses as much as possible not only when low polluted waters such as well water and the like are used as the drinking water for human, but also when they are used as the drinking water for livestock in the field of stockbreeding or for irrigation in the field of agriculture or horticulture.
Thus, for example, when iron contents are to be removed from a well water, there has been no other way of purification but to add an oxidizing agent to the well water to convert the ionized iron to iron oxide, which is then aggregated using a high polymer and removed by sedimentation and filtration. In this case, large-scale equipments including sedimentation tanks, filtration tanks, etc. are necessary, leading to extreme elevation of production cost and running cost of the facility, disadvantageously. Meanwhile, in the method in which an oxidizing agent is used for water purification, although the iron contents can be converted into iron oxide, it is not very effective for removing manganese. Namely, while an underground water containing a large amount of iron contents generally contains a large amount of manganese, and if the iron contents only can thus be removed from the waters, the manganese must be removed by carrying out another treatment, requiring large-scale equipments and a high cost for the extra treatment, under the present circumstances. Further, the low polluted water generally contains frequently very fine organic suspended matters in addition to the heavy metals such as iron and manganese, and the organic suspended matters are difficult to remove using a coagulant. Accordingly, a sand or active carbon filter must be used for adsorbing and filtering off the organic suspended matters thereon. However, if the adsorption capacity of the filter is reduced, the water from which the pollutive components are not fully removed comes to be supplied. Besides, the filter must be replaced periodically, leading to cost elevation, and if such replacement of filter is neglected, the unpurified water comes to be supplied, inconveniently.
Therefore, this invention is proposed in view of various troubles brought about by the low polluted water (e.g. well water and insufficiently treated water supplied from a water purifying station) in which inadequate matters including heavy metals, such as iron contents, manganese and very fine suspended matters are concurrently or selectively contained and overcoming them successfully, and it is an object of the invention to provide a process for purifying a low polluted water containing inadequate matters typified by the iron contents to high purity using very simple means, as well as, an apparatus for practicing the process.